<div class="cards-content">
  <!-- // 如何动态的再赋值一个class？ -->
  <div class="card-item first" *ngFor="let item of data, let i = index" [ngClass]="{first: i === 0}">
    <div class="num-unit">
      <div class="num">{{item.value}}</div>
      <div class="unit">{{item.unit}}</div>
    </div>
    <div class="tag">
      <span>
        <!-- 请更换成type -->
        {{item.type}}
      </span>
    </div>
  </div>
</div>